This invention relates to a communication system utilizing optical fibers and, more particularly, to a unit that functions as an interface between incoming and outgoing fibers and individual customers connected to the system.
Due primarily to their low-loss and high-bandwidth characteristics, optical fibers are utilized in a wide variety of communication systems of practical importance. For some time, such utilization has been seen as particularly attractive in long-haul systems. Although relatively expensive terminal equipment is typically required in a long-haul system, the cost of the equipment is in effect shared by tens of thousands of individual customers served by the system.
More recently, considerable development effort has been directed at trying to devise economical optical-fiber systems capable of delivering broadband signals (for example, voice, data and video) directly to customer premises. One such approach involves running optical fiber from a central office to each customer location and providing a so-called optical network unit between the fiber and the customer. An incoming optical signal can be thereby constantly applied from the central office to each network unit. In each unit, the incoming optical signal is split into two portions. One portion is detected and then applied as an electrical signal to the customer equipment. Another portion of the incoming optical signal is modulated with electrical signals from the customer and then sent in the form of an outgoing optical signal back to the central office.
Significantly, the aforedescribed optical network unit does not require an optical source such as a laser. The only optical source in the overall system is typically located in the central office. Accordingly, the need for wavelength control and timing accuracy at each customer location is thereby obviated.
Nevertheless, optical network units as heretofore envisioned are relatively large and costly. A straightforward approach to the design of such a unit that includes an optical splitter, a photodetector, a modulator and an electrical amplifier involves simply interconnecting conventional discrete components. The resulting multi-component unit, however, is typically relatively bulky and expensive and requires, for example, four fiber connectors and three electrical connectors.
Accordingly, considerable efforts have been directed by workers skilled in the art aimed at attempting to develop an optical network unit that is characterized by relatively low cost, compactness, simplicity and reliability. It was recognized that these efforts, if successful, could provide an important practical basis for achieving economical broadband service to individual customers.